Anabaena Is a Cyanobacterium with Two Types of Cells

question 23

Multiple Choice

Anabaena is a cyanobacterium with two types of cells. One type of cell can carry out photosynthesis and the other type can carry out nitrogen fixation. However, the oxygen produced by photosynthesis inhibits the enzymes for nitrogen fixation. Which structural characteristic allows the nitrogen-fixing cells to continue to function?

• A) modified plasma membranes that are impermeable to both oxygen and nitrogen
• B) cell walls that are impermeable to both oxygen and nitrogen
• C) specialized cells called heterocysts, which have cell walls that restrict the entry of oxygen
• D) plasma membranes that are impermeable to nitrogen